1. Field of the Invention
The present invention relates to a developing roller, a developing apparatus using the developing roller, and the image forming apparatus, which are used in an image forming apparatus and the like such as a copying machine and a laser printer.
2. Description of the Related Art
In a copying machine using an electrophotographic system, a facsimile, and a printer, a photosensitive member is uniformly charged by a charging roller, thereby forming an electrostatic latent image by a laser and the like. Next, a developer inside a developing container is uniformly coated on the developing roller at a proper charge by a developer coating roller and a developer controlling member, and a transfer (developing) of the developer is performed at a contact portion with the photosensitive member and the developing roller. After that, the developer on the photosensitive member is transferred on a recording paper by a transfer roller, and is fixed by heat and pressure, and the developer remaining on the photosensitive member is removed by a cleaning blade, thereby completing a series of the processes.
As the characteristics required for these developing rollers used for the image forming apparatus, (1) a uniform and high electrostatic property toward the developer, and (2) a uniform developer conveying property are cited.
In the developing roller having a shaft, an elastic layer formed on the outer periphery of the shaft, and at least one layer of a resin coated layer formed on the outer periphery of the elastic layer, it is proposed to improve the above-described characteristics by diffusing various fine particles into the resin coated layer (Japanese Patent Application Laid-Open Nos. 2004-191561, 2005-258201, 2005-115265, and H11-212354).
Now, accompanied with the recent high quality image of the image forming apparatus, the developer used in the image forming apparatus has advanced in making the particle diameter extremely small. To make the average particle diameter of the developer extremely small is an effective means to improve particularly granularity and character reproducibility from among the image quality characteristics. However, much needs to be improved in a specific image quality item, particularly, a fog and a stripe-like image defect (hereinafter, referred to as resulting stripe from development) at the continuous printing time.
That is, when the developer is made into an extremely small particle, the number of contacts/collisions of the fellow developers or the developer with the developing roller and the developer controlling member is increased, and the developer is liable to deteriorate. The deteriorated developer is easily fused on the surfaces of the developing roller and the developer controlling member. The developing roller fused with the deteriorated developer on the surface is reduced in the charge imparting amount to the developer, and as a result, the fog is often generated in the electrophotographic image. Further, when the deteriorated developer is partially fused on the surface of the developer controlling member, a coating amount of the developer on the developing roller is liable to be non-uniform. As a result, the resulting stripe from development is often generated in the electrophotographic image.
Further, in the recent years, even in a color image forming apparatus having many outputs of so-called solid images, further uniformity of the image and elevated concentration of the image density are required.
For such requirement, a developing apparatus is proposed in which a bias is applied on a developing blade for regulating an amount of the developer on the developing roller (for example, Japanese Patent Application Laid-Open No. 2000-112212).
However, by applying a bias on the developer controlling member (developing blade), similarly to a case of making the particle diameter of the toner extremely small, the generation of the fog and the resulting stripe from development at a continuous printing time has become often conspicuous. That is, the application of the bias on the developing blade increases a stress given to the developer, and the fusion of the developer and an external additive of the developer on the developing roller surface and the developing blade easily generate the fog and the resulting stripe from development.
As described above, as a result of repeated examinations in consideration of the recent technical trend such as making the developer extremely small and applying a bias on the developing blade, in which the fog and the resulting stripe from development are easily generated on the electrophotographic image, it was found that the developing rollers proposed heretofore such as disclosed in Japanese Patent application Laid-Open Nos. 2004-191561, 2005-258201, 2005-115265, and H11-212354 had often generated the fog and the resulting stripe from development on the electrophotographic image particularly at the continuous printing time in the low temperature and low-humidity environment.